Continuously variable ratio transmissions are employed in vehicles to provide efficient drive systems. The transmission ratio can be changed in a continuous manner from a maximum underdrive ratio to a maximum overdrive ratio. This permits the engine to be operated at either the best fuel consumption area or the best performance area. Vehicle speed can be maintained at a substantially constant level while the transmission ratio is varied to attain a desired vehicle speed as requested by an operator.
The most currently used continuously variable transmissions are the flexible belt type due mainly to the advent of the flexible steel belt which runs against steel sheaves. The sheaves of the input and output pulleys are movable axially to adjust the radius at which the belt turns. The sheaves are moved to hydraulic pressure which is distributed from a control valve.